# Getting frequency/spectrum from audio

Hi, i want to get the current freuency/spectrum from the AudioNode, how can i achieve that?
I found this one link, but i don’t get it what this guy is meaning at all.
My goal is something like that: [video]http://www.youtube.com/watch?v=nuHmMh3vXhU[/video]

kind regards
sytrox

Well if you don’t know what FFT is you will probably have a hard time doing that…

To not come across like an asshole by just saying that, heres some FFT code that might be helpful as soon as you know how

[java]/*************************************************************************

• Compilation: javac FFT.java
• Execution: java FFT N
• Dependencies: Complex.java
• Compute the FFT and inverse FFT of a length N complex sequence.
• Bare bones implementation that runs in O(N log N) time.
• Limitations

• assumes N is a power of 2
• not the most memory efficient algorithm

*************************************************************************/

package kleinehummel;

/**
*

• @author normenhansen
*/

public class FFT {

``````// compute the FFT of x[], assuming its length is a power of 2
public static Complex[] fft(Complex[] x) {
int N = x.length;
Complex[] y = new Complex[N];

// base case
if (N == 1) {
y[0] = x[0];
return y;
}

// radix 2 Cooley-Tukey FFT
if (N % 2 != 0) throw new RuntimeException("N is not a power of 2");
Complex[] even = new Complex[N/2];
Complex[] odd  = new Complex[N/2];
for (int k = 0; k < N/2; k++) even[k] = x[2*k];
for (int k = 0; k < N/2; k++) odd[k]  = x[2*k + 1];

Complex[] q = fft(even);
Complex[] r = fft(odd);

for (int k = 0; k < N/2; k++) {
double kth = -2 * k * Math.PI / N;
Complex wk = new Complex(Math.cos(kth), Math.sin(kth));
y[k]       = q[k].plus(wk.times(r[k]));
y[k + N/2] = q[k].minus(wk.times(r[k]));
}
return y;
}

// compute the inverse FFT of x[], assuming its length is a power of 2
public static Complex[] ifft(Complex[] x) {
int N = x.length;

// take conjugate
for (int i = 0; i < N; i++)
x[i] = x[i].conjugate();

// compute forward FFT
Complex[] y = fft(x);

// take conjugate again
for (int i = 0; i < N; i++)
y[i] = y[i].conjugate();

// divide by N
for (int i = 0; i < N; i++)
y[i] = y[i].times(1.0 / N);

return y;

}

// compute the convolution of x and y
public static Complex[] convolve(Complex[] x, Complex[] y) {
if (x.length != y.length) throw new RuntimeException("Dimensions don't agree");
int N = x.length;

// compute FFT of each sequence
Complex[] a = fft(x);
Complex[] b = fft(y);

// point-wise multiply
Complex[] c = new Complex[N];
for (int i = 0; i < N; i++)
c[i] = a[i].times(b[i]);

// compute inverse FFT
return ifft(c);
}

// test client
public static void main(String[] args) {
int N = 128;
//double start=.getTimeInMillis();

Complex[] x = new Complex[N];

// original data
for (int i = 0; i < N; i++) {
x[i] = new Complex(i, 0);
}
for (int i = 0; i < N; i++)
System.out.println(x[i]);
System.out.println();

// FFT of original data
Complex[] y = fft(x);
for (int i = 0; i < N; i++)
System.out.println(y[i]);
System.out.println();

// take inverse FFT
Complex[] z = ifft(y);
for (int i = 0; i < N; i++)
System.out.println(z[i]);
System.out.println();

// convolution of x with itself
Complex[] c = convolve(x, x);
for (int i = 0; i < N; i++)
System.out.println(c[i]);

}
``````

}
[/java]

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